The present invention relates to a color cathode ray tube, and in particular to a color cathode ray tube having a so-called slot type shadow mask.
A color cathode ray tube used for a TV receiver, or a monitor for a personal computer or other information equipment is formed of a vacuum envelope comprising a face panel having a mosaic phosphor screen coated with plural-color phosphors (usually red, green and blue), a neck housing an electron gun and a funnel for connecting the neck to the face panel.
A deflection yoke is mounted around the outside of the transition region between the funnel and the neck, and intensity-modulated electron beams emitted from the electron gun are scanned horizontally and vertically on the phosphor screen by horizontal and vertical deflection magnetic fields generated by the deflection yoke to reproduce an image.
A shadow mask is closely spaced from the phosphor screen, and serves as a so-called color selection electrode for making each of a plurality of electron beams (usually three beams for red, green and blue, respectively) emitted from the electron gun impinge on only phosphor elements of a corresponding color.
Various types of shadow masks are known, and among them is a slot type shadow mask having a plurality of strips (long narrow pieces) extending in a direction perpendicular to a horizontal scanning direction of the electron beams emitted from the electron gun and a plurality of bridge portions for connecting two adjacent strips such that each of rectangular electron beam apertures (which are called xe2x80x9cslotsxe2x80x9d) is defined by two adjacent strips and two adjacent bridge portions. This slot type shadow mask is tensed along the direction perpendicular to the horizontal scanning direction of the electron beams, for example, and it is known that it vibrates when an external shock is applied to it. If the shadow mask vibrates, the position of the electron beams passing through a slot is deviated, and thereby landing positions of the electron beams are deviated from their intended phosphor elements and the reproduced image also vibrates resulting in deterioration of image quality. Further, there is a case in which this vibration damages the shadow mask itself and therefore it is impossible to reproduce a normal image.
To prevent such vibration of the shadow mask, there is a technique to superpose a vibration-preventing wire on a slit extending in the direction perpendicular to the horizontal scanning direction of the electron beams (the vertical direction) and thereby to absorb the vibration, as disclosed in Japanese Patent Application Laid-open No. Hei 8-227,667.
FIG. 14 is a schematic perspective view of a prior art slot type shadow mask provided with a vibration-preventing structure. A shadow mask 8 is depicted as a constituent component of a shadow mask structure 7 stretched over mask frames 9a, 9b. 
The pair of mask frames 9a, 9b are fixed to support frames 10a, 10b to form a peripheral frame, and the shadow mask 8 is stretched over the mask frames 9a, 9b. In the shadow mask 8, a large number of slot type electron beam apertures 20 are defined by a plurality of strips 21 extending in a direction (the Y-axis direction) perpendicular to a horizontal scanning direction (the X-axis direction) of the electron beams emitted from the electron gun and a plurality of bridge portions 22 for connecting two adjacent strips 21 to form an apertured area.
Vibration-preventing wires 12 are superposed on the respective strips 21 in a direction in which the strips 21 extend, and are fixed to the wire supports 11a attached to the mask frames 9a, 9b. The wire supports 11a are made of resilient material and apply a desired tension to the vibration-preventing wires 12.
On the other hand, Japanese Patent Application Laid-open No. Hei 5-198,271 discloses a color cathode ray tube in which a shadow mask comprised of strips only without no bridges (i.e., a shadow mask formed of a parallel array of narrow strips held together only at the ends) and a vibration-preventing wire is stretched over a surface of the shadow mask in the horizontal scanning direction and is pressed against the surface of the shadow mask to attenuate the vibration as much as possible. Incidentally, a plurality of vibration-preventing wires of this type are usually disposed in the horizontal scanning direction of the electron beams.
In the prior art shadow mask, it is difficult to make the vibration-preventing wire contact the surface of the shadow mask securely, and it is also inevitable for the vibration-preventing wire to be disposed to traverse the electron beam apertures.
Therefore, there have been pointed out problems that vibration of the shadow mask caused by external shock do not attenuate in a short period of time, or a horizontal black line appears in a reproduced image due to shadow in a phosphor screen caused by collision with the vibration-preventing wire, of the electron beams which are intended to pass through the electron beam apertures, resulting in deterioration of image quality.
It is an object of the invention to provide a color cathode ray tube having vibration of the shadow mask prevented without incurring deterioration in the image quality by eliminating the above problems with the prior art.
To achieve the above objects, in a shadow mask of the present invention, holes for positioning a vibration-preventing wire are opened at positions corresponding to ends of the strips, outside an apertured area of the shadow mask, and the vibration-preventing wire is passed through the holes and stretched.
The representative configurations of the present invention are as follows:
In accordance with the present invention, there is provided a color cathode ray tube comprising a vacuum envelope including a panel, a neck and a funnel for connecting the panel and the neck, an electron gun housed in the neck, a phosphor screen coated on an inner surface of the panel, and a shadow mask closely spaced from the phosphor screen and housed in the panel, the shadow mask having a plurality of strips extending in a direction perpendicular to a horizontal scanning direction of electron beams emitted from the electron gun and a plurality of bridge portions connecting adjacent ones among the plurality of strips, the shadow mask being formed with an apertured area having a plurality of slot-shaped electron beam apertures therein, each of the plurality of slot-shaped electron beam apertures being defined by two adjacent ones among the plurality of strips and two adjacent ones in the direction perpendicular to the horizontal scanning direction among the plurality of bridge portions, the shadow mask being provided with at least one wire held under tension in the extending direction of the plurality of strips so as to be superposed on a surface of one of the plurality of strips in the apertured area, and the surface of the one of the plurality of strips being a surface of the one of the plurality of strips facing the electron gun.
In accordance with the present invention, there is provided a color cathode ray tube comprising a vacuum envelope including a panel, a neck and a funnel for connecting the panel and the neck, an electron gun housed in the neck, a phosphor screen coating on an inner surface of the panel, and a shadow mask closely spaced from the phosphor screen and housed in the panel, the shadow mask having a plurality of strips extending in a direction perpendicular to a horizontal scanning direction of electron beams emitted from the electron gun and a plurality of bridge portions connecting adjacent ones among the plurality of strips, the shadow mask being formed with an apertured area having a plurality of slot-shaped electron beam apertures therein, each of the plurality of slot-shaped electron beam apertures being defined by two adjacent ones among the plurality of strips and two adjacent ones in the direction perpendicular to the horizontal scanning direction among the plurality of bridge portions, the shadow mask being provided with at least one wire held under tension in the extending direction of the plurality of strips so as to be superposed on a surface of one of the plurality of strips in the apertured area, the surface of the one of the plurality of strips being a surface of the one of the plurality of strips facing the electron gun, and both ends made of the at least one wire being brought out through holes opened onto a surface of the shadow mask facing the phosphor screen.
The strips of the shadow mask extend in a direction perpendicular to the horizontal scanning direction of the electron beams emitted from the electron gun, and therefore the vibration-preventing wire do not traverse the electron beam apertures and is disposed to be superposed on the strip.
Consequently, the shadow of the vibration-preventing wire is not projected on the phorphor, and therefore a high-quality image is obtained.
Further, by superposing the vibration-preventing wire so as to extend in an extending direction of the strips on a surface of a side of a strip which is convex in the extending direction of the strips, the vibration-preventing wire is pressed against the strip with the vibration-preventing wire in solid contact with the strip and provides an extremely great vibration-preventing effect.
Further, a plurality of the vibration-preventing wires can be arranged in the horizontal scanning direction of the electron beams, but the strips are connected together and integrally with the bridge portions, and therefore even a single vibration-preventing wire provides a vibration-preventing effect to vibration of the surface of the shadow mask.
It is needless to say the present invention is not limited to the above configurations or embodiments to be described subsequently, but various changes can be made without departing from the spirit of the present invention.